A bicycle rider sits on the seat which is connected to the seat tube of the bicycle frame and vibration transferred from the ground is transferred to the rider via the tires, the wheels, the seat tube and the seat post. However to reduce the vibration transferred to the rider is one of the main concerns to the bicycle manufacturers. Besides, the height of the seat is related to safety and comfortable riding to the riders of different heights. Therefore, an adjustable bicycle seat assembly is developed to meet the requirements and disclosed in U.S. Pat. No. 7,083,180 which discloses a seat post adjustably inserted into the seat tube of the bicycle frame and a separation member is located between the seat post and the seat tube. An opening is defined in the separation member and an axle extends through the opening and the other end of the axle is connected to a movable member in the seat tube. The axle is moveable between the first position and the second position, and the seat tube and the seat post are moved relative to each other so as to control the travel path of the fluid which is filled in the second position and air is filled in the first position. The fluid flows when the opening is opened so as to compress the air to adjust the relative position of the seat post and the seat tube. However, the seat tube and the seat post are both circular tubes which rotate relative each other. The seat rotates especially when vibration is transferred to the rider and the rider cannot concentrate to operate the handlebar of the bicycle.
The present invention intends to provide an adjustable bicycle seat assembly wherein the seat post is adjusted relative to the seat tube of the bicycle frame and the seat post is not rotated relative to the seat tube.